This invention relates to a valve driving means for V-type engines for vehicles and more particularly to an improved camshaft drive arrangement for such engines.
In high performance engines, it is well recognized that it is desirable to provide two overhead driven camshafts for operating the intake and exhaust valves of the engine. Generally, the intake valves all lie on one side of the cylinder head and are operated by an intake camshaft and the exhaust valves all lie on the other side and are driven by an exhaust camshaft. Such an arrangement is highly favored in connection with high performance engines. The use of two such positioned camshafts, however, gives rise to certain problems in connection with the driving of the camshafts. The mechanism for driving the camshafts in timed relationship with the crankshaft can add significantly to the overall length of the engine and present certain problems in connection with servicing. These problems are somewhat magnified when the camshafts are driven by rubber belts rather than chains. When belt driven, the driving belt is normally positioned externally of the engine and this can significantly add to the length of the engine. With the present emphasis toward compact engine compartments for vehicles, this can give rise to certain problems. In addition, the transverse positioning of engines in some vehicles can further complicate this problem, particularly when the engine is juxtaposed to the suspension system of the associated driven wheels.
There are a number of other accessories associated with the engine that are also driven by belts such as the alternator or generator, power steering pumps, air conditioning compressors, and other such components. The positioning of these belts in addition to the timing belts can give rise to further spacial problems and also can unduly complicate the servicing of individual belts of the engine.
The problems aforenoted are further emphasized when the engine has banks of cylinders that are not aligned with each other such as with V-type or opposed engines. This is particularly true when the cylinder banks each support pairs of overhead mounted camshafts. The additional complexities of the driving of all of these camshafts and the other accessories that are driven by belts from the engine crankshaft can be readily imagined. Also, it is desirable to minimize the overhang length of the driven sprockets of the various camshafts so as to simplify the bearing loading of them and to reduce the amount of cantilevered condition of the camshaft.
It is, therefore, a principal object of this invention to provide an improved camshaft drive arrangement for an internal combustion engine.
It is another object of this invention to provide an improved camshaft drive arrangement for internal combustion engines that simplifies the overall construction.
It is another object of this invention to provide a compact camshaft drive arrangement for an internal combustion engine so as to facilitate application in a motor vehicle.
It is a yet further object of this invention to provide an improved belt driven camshaft arrangement for V-type engines wherein servicing and interference between the various belts is substantially minimized.
A first feature of this invention is adapted to be embodied in a camshaft drive for an internal combustion engine comprising first and second camshafts supported for rotation about parallel and offset axes. The engine has an output shaft and first timing drive means drive the first camshaft directly from the output shaft. Second timing drive means are provided for driving the second camshaft from the first camshaft.
Another feature of the invention is adapted to be embodied in an internal combustion engine having a crankcase, a crankshaft journaled in the crankcase and a pair of angularly disposed cylinders extending from the crankcase and forming combustion chambers at the ends spaced from the crankcase. A first camshaft is supported for rotation about an axis parallel to the crankshaft axis and is associated with the combustion chamber of one of the cylinders for operating valves associated with that cylinder. A second camshaft is supported for rotation about an axis parallel to and offset from the crankshaft axis and the first camshaft axis and is associated with the combustion chamber of the other of the cylinders for operating valves associated with that other cylinder. First timing means drive the first camshaft in timed relationship with the crankshaft at one end of the first camshaft. Second timing means are provided for driving the second camshaft in timed relationship with the crankshaft at the opposite end of the second camshaft.